Field of the Invention
The present invention relates to a colored resin particle dispersion, a method for producing the colored resin particle dispersion, and an inkjet ink.
Description of the Related Art
Colored resin particle dispersions are used as components for printing inks for all manner of printing methods.
The colorants for printing inks can be broadly classified into dyes and pigments. Using a dye offers the advantage of particularly favorable color development. Further, compared with pigments, dyes offer the advantage of superior abrasion resistance, and particularly superior rub fastness. However, dyes themselves exhibit inferior water resistance and marker resistance. On the other hand, pigments offer the advantages of high image density and excellent weather resistance, but exhibit inferior abrasion resistance, and particularly rub fastness, compared with dyes.
In light of these properties, a method has been proposed in which by encapsulating the colorant within a resin to form colored resin particles, an ink can be provided which exhibits excellent abrasion resistance, water resistance and marker resistance, while retaining the image-forming properties of the colorant.
Patent Document 1 and Patent Document 2 each proposes the production of a polymer particle dispersion in which by using an organic solvent A and an organic solvent B having almost no compatibility with the organic solvent A, forming a dispersion composed of a dispersed phase containing the organic solvent B and a resin and a continuous phase containing the organic solvent A, and then removing the organic solvent B from the dispersion under reduced pressure or heating, a polymer particle dispersion is produced containing polymer particles dispersed in the organic solvent A.
However, the above documents did not investigate the abrasion resistance of images obtained by preparing a printing ink using this type of polymer particle dispersion and then printing the ink onto paper or the like. It is difficult to obtain satisfactory image abrasion resistance simply by adding a resin to the ink. Further, another problem arises in that if the colorant is added in an amount sufficient to obtain satisfactory coloration vividness for the printed image, then the viscosity of the polymer particle dispersion increases, making preparation of the dispersion difficult.
Patent Document 3 proposes colored resin particles prepared by dispersing a dispersion phase containing a non-aqueous solvent B, a dye, a resin and an acidic dispersant in a continuous phase containing a non-aqueous solvent A and a basic dispersant to prepare an oil-in-oil emulsion, and then removing the non-aqueous solvent B from this oil-in-oil emulsion.
Patent Document 3 discloses that by using a basic dispersant in the continuous phase and an acidic dispersant in the dispersion phase, the oil-in-oil emulsion can be prepared with excellent emulsion stability regardless of the type of resin used, and a colored resin particle dispersion can be prepared which exhibits excellent water resistance, marker resistance and rub fastness.
Patent Document 4 proposes a method for producing a liquid developer for an electrophotographic method, the method comprising adding a colored resin to a non-polar dispersion medium, heating the non-polar dispersion medium under stirring to at least the softening point of the resin, and then cooling and solidifying the thus obtained resin emulsion.
Patent Document 4 proposes the addition of an oil-soluble surfactant to the non-polar dispersion medium.
Patent Document 5 proposes a method for producing a resin emulsion suitable for producing a toner, the method comprising melting and mixing a resin, adding a surfactant to the resin, adding a basic reagent and water to the resin, and performing ultrasonic mixing. Patent Document 5 also proposes adding a toner composition to the resin, performing a phase inversion to prepare a phase inversion emulsion comprising a dispersed phase containing the melted resin and the toner composition, and then solidifying toner-sized liquid droplets to obtain toner particles.                Patent Document 1: JP 2007-197632 A        Patent Document 2: JP 2005-255911 A        Patent Document 3: JP 2014-019770 A        Patent Document 4: JP H09-179354 A        Patent Document 5: JP 2010-248511 A        
In Patent Documents 1 to 3, colored resin particle dispersions are obtained via a step of preparing an oil-in-oil emulsion, and a step of removing a low-boiling point solvent from the oil-in-oil emulsion. As a result, because the dispersed phase is prepared by dissolving the resin in a low-boiling point solvent, a problem arises in that the film of the obtained printed item has low resistance relative to the low-boiling point solvent. In particular, in those cases where a lower alcohol solvent is use as the low-boiling point solvent, the alcohol resistance of the printed film becomes a problem. Further, another problem arises in that the production facilities used for the solvent removal and other handling of the low-boiling point solvent require explosion-proof production facilities.
Patent Document 4 proposes a method for producing a liquid developer by using a resin emulsion to prepare a resin particle dispersion. However, in liquid developers for electrophotographic methods, the volume-average particle size of the resin particles is comparatively large. Patent Document 4 discloses an average particle size of 1.5 to 5.0 μm. Further, in liquid developers for electrophotographic methods, the resin particle solid fraction concentration is comparatively low, and no investigations have been conducted into the effects of the types and amounts of the colorant and the resin on the viscosity of the dispersion.
Patent Document 5 proposes a method for producing an aqueous resin emulsion that is suitable for producing a toner. In an aqueous resin emulsion, the resin particles can be dispersed using ionic repulsion. However, if an aqueous resin emulsion is used without further modification as an ink, then because the ink is water-based, paper curling caused by the moisture becomes a problem. Further, if the resin fraction is extracted from the aqueous resin emulsion and dispersed in a non-aqueous solvent, then the extracted resin fraction tends to aggregate, and dispersion in the non-aqueous solvent becomes difficult.
An object of the present invention is to provide a colored resin particle dispersion and an inkjet ink which exhibit excellent rub fastness and alcohol resistance, and yield printed items having high image density.